A capacitor is a passive electronic component that is used to store energy in the form of an electrostatic field, and comprises a pair of electrodes separated by a dielectric layer. When a potential difference exists between two electrodes, an electric field is present in the dielectric layer. In practice, the dielectric layer between electrodes passes a small amount of leakage current.
A characteristic electric field known as the breakdown strength Ebd, is an electric field in which the dielectric layer in a capacitor becomes conductive. Voltage at which this occurs is called the breakdown voltage of the device, and is given by the product of dielectric strength and separation between the electrodes,Vbd=Ebdd
The maximal volumetric energy density stored in the capacitor is limited by the value proportional to ˜ε·E2bd, where E is dielectric permittivity and Ebd is breakdown strength. Thus, in order to increase the stored energy of the capacitor it is necessary to increase dielectric permeability ε and breakdown strength Ebd of the dielectric layer.
For high voltage applications, much larger capacitors have to be used. There are a number of factors that can dramatically reduce the breakdown voltage. Geometry of the conductive electrodes is important for these applications. In particular, sharp edges or points hugely increase the electric field strength locally and can lead to a local breakdown. Once a local breakdown starts at any point, the breakdown will quickly “trace” through the dielectric layer till it reaches the opposite electrode and causes a short circuit.
Breakdown of the dielectric layer usually occurs as follows. Intensity of an electric field becomes high enough free electrons from atoms of the dielectric material and make them conduct an electric current from one electrode to another. Presence of impurities in the dielectric or imperfections of the crystal structure can result in an avalanche breakdown as observed in semiconductor devices.
Other important characteristic of a dielectric material is its dielectric permittivity and resistivity. Different types of dielectric materials are used for capacitors and include ceramics, polymer film, paper, and electrolytic capacitors of different kinds. The most widely used polymer film materials are polypropylene and polyester. Increase of dielectric permittivity while maintaining high resistivity of film capacitor dielectrics allows increasing of volumetric energy density which makes it an important technical task.
An ultra-high dielectric constant composite of polyaniline, PANI-DBSA/PAA, was synthesized using in situ polymerization of aniline in an aqueous dispersion of poly-acrylic acid (PAA) in the presence of dodecylbenzene sulfonate (DBSA) (see, Chao-Hsien Hoa et al., “High dielectric constant polyaniline/poly(acrylic acid) composites prepared by in situ polymerization”, Synthetic Metals 158 (2008), pp. 630-637). The water-soluble PAA served as a polymeric stabilizer, protecting the PANI particles from macroscopic aggregation. A very high dielectric constant of ca. 2.0*105 (at 1 kHz) was obtained for the composite containing 30% PANI by weight. Influence of the PANI content on the morphological, dielectric and electrical properties of the composites was investigated. Frequency dependence of dielectric permittivity, dielectric loss, loss tangent and electric modulus were analyzed in the frequency range from 0.5 kHz to 10 MHz. SEM micrograph revealed that composites with high PANI content (i.e., 20 wt. %) consisted of numerous nano-scale PANI particles that were evenly distributed within the PAA matrix. High dielectric constants were attributed to the sum of the small capacitors of the PANI particles. The drawback of this material is a possible occurrence of percolation and formation of at least one continuous conductive path under electric field with probability of such an event increasing with an increase of the electric field. When at least one continuous path (track) through the neighboring conducting PANI particles is formed between electrodes of the capacitor, it decreases a breakdown voltage of such capacitor.
Colloidal polyaniline particles stabilized with a water-soluble polymer, poly(N-vinylpyrrolidone) [poly(1-vinylpyrrolidin-2-one)], have been prepared by dispersion polymerization. The average particle size, 241±50 nm, have been determined by dynamic light scattering (see, Jaroslav Stejskal and Irina Sapurina, “Polyaniline: Thin Films and Colloidal Dispersions (IUPAC Technical Report)”, Pure and Applied Chemistry, Vol. 77, No. 5, pp. 815-826 (2005).
Single crystals of doped aniline oligomers are produced via a simple solution-based self-assembly method (see, Yue Wang, et. al., “Morphological and Dimensional Control via Hierarchical Assembly of Doped Oligoaniline Single Crystals”, J. Am. Chem. Soc. 2012, 134, pp. 9251-9262). Detailed mechanistic studies reveal that crystals of different morphologies and dimensions can be produced by a “bottom-up” hierarchical assembly where structures such as one-dimensional (1-D) nanofibers can be aggregated into higher order architectures. A large variety of crystalline nanostructures, including 1-D nanofibers and nanowires, 2-D nanoribbons and nanosheets, 3-D nanoplates, stacked sheets, nanoflowers, porous networks, hollow spheres, and twisted coils, can be obtained by controlling the nucleation of the crystals and the non-covalent interactions between the doped oligomers. These nanoscale crystals exhibit enhanced conductivity compared to their bulk counterparts as well as interesting structure-property relationships such as shape-dependent crystallinity. Furthermore, the morphology and dimension of these structures can be largely rationalized and predicted by monitoring molecule-solvent interactions via absorption studies. Using doped tetra-aniline as a model system, the results and strategies presented in this article provide insight into the general scheme of shape and size control for organic materials.
There is a known a multilayer structure comprising blocking and dielectric layers. The first blocking layer is disposed on a dielectric layer, and the second blocking layer is disposed under a dielectric layer. Dielectric constants of the first and second blocking layers are both independently greater than the dielectric constant of the dielectric layer. A drawback of this device is that blocking layers of high dielectric permittivity can lead to destruction of the energy storage device. Materials with high dielectric permittivity which are based on composite materials and containing polarized particles (such as PANI particles) might demonstrate a percolation phenomenon. The formed polycrystalline structure of layers has multiple dangling chemical bonds on borders between crystallites. When the used material with high dielectric permittivity possesses polycrystalline structure percolation might occur along the borders of crystal grains. Another drawback of the known device is an expensive manufacturing procedure which is vacuum deposition of all layers.
The present invention solves a problem of the further increase of volumetric and mass density of reserved energy of the metacapacitor as energy storage device and based on disclosed solid multilayer structure, and at the same time reduces cost of materials and manufacturing process.